Metric-system-related events and anniversaries

Those highlighted in yellow are sponsored by various organizations and are generally observed each year, while the others are not formally observed but are anniversaries that might be of interest.

March

1st week — Weights and Measures Week — The National Conference on Weights and Measures (NCWM) sponsors a national Weights and Measures Week during the first full week of March, to celebrate “the trust that is built into every transaction by a national, local and state weights and measures system.”

April

5 — Mendenhall Order — On 5 April 1893, the Mendenhall Order was issued, declaring the meter and kilogram to be the fundamental standards of length and mass in the US and defining the inch-pound units in terms of the metric system.

May

20 — World Metrology Day — On 20 May 1875, the Convention du Mètre, also known as the Metric Convention, Metrical Convention, Metre Convention, Convention of the Metre, or Treaty of the Meter, was signed by 17 countries, including the US. To recognize its anniversary, 20 May is World Metrology Day.

July

28 — Metric Act of 1866 — On 28 July 1866 the Metric Act of 1866, which legally recognized the metric system of measurement in the US, was enacted.

23 — Mole Day — An unofficial holiday to celebrate Avogadro’s number, 6.02×10²³, the number of entities in a mole of a substance. “Mole Day” was originally suggested by an early 1980’s article in The Science Teacher; for more information see the National Mole Day Foundation and read Wikipedia’s article about Mole Day.

December

23 — Metric Conversion Act of 1975 — On 23 December 1975 the Metric Conversion Act of 1975 was enacted. Among other things, it designated the metric system as the preferred system of weights and measures for the US.